Variable Density Scanning

ABSTRACT

Systems and techniques for varying a scan rate in a measurement instrument. The techniques may be used in scanning probe instruments, including atomic force microscopes (AFMs) and other scanning probe microscopes, as well as profilometers and confocal optical microscopes. This allows the selective imaging of particular regions of a sample surface for accurate measurement of critical dimensions within a relatively small data acquisition time.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of Ser. No. 11/563,822, filed Jan. 31, 2006,which claims the benefit of priority of U.S. Provisional PatentApplication Ser. No. 60/763,659, entitled VARIABLE DENSITY SCANNING,filed on Jan. 31, 2006, which is hereby incorporated by reference in itsentirety.

TECHNICAL FIELD

This invention generally relates to certain measurement instruments,including cantilever-based instruments and scanning probe instruments,such as atomic force microscopes (AFMs).

BACKGROUND

For the sake of convenience, the current description focuses primarilyon systems and techniques that may be realized in a particular type ofcantilever-based instrument: the AFM.

Cantilever-based instruments include such instruments as AFMs, molecularforce probe instruments (1D or 3D), high-resolution profilometers(including mechanical stylus profilometers), surface modificationinstruments, chemical or biological sensing probes, and micro-actuateddevices. The systems and techniques described herein may be realized insuch other cantilever-based instruments and may also be used with otherscanning probe instruments. For example, they may be used with scanningoptical probes such as optical confocal microscopes.

An AFM is a device used to produce images of surface topography (and/orother sample characteristics) based on information obtained fromscanning (e.g., rastering) a sharp probe on the end of a cantileverrelative to the surface of the sample. Topographical and/or otherfeatures of the surface are detected by detecting changes in cantileverdeflection and/or oscillation characteristics (e.g., by detecting smallchanges in deflection, phase, frequency, etc., and using feedback toreturn the system to a reference state). By scanning the probe relativeto the sample, a “map” of the sample topography or other samplecharacteristics may be obtained.

Changes in deflection or in oscillation are typically detected by anoptical lever arrangement whereby a light beam is directed onto acantilever in the same reference frame as the optical lever. The beamreflected from the cantilever illuminates a position sensitive detector(PSD). As the deflection or oscillation of the cantilever changes, theposition of the reflected spot on the PSD changes, causing a change inthe output from the PSD. Changes in the deflection or oscillation of thecantilever are typically made to trigger a change in the verticalposition of the cantilever base relative to the sample, in order tomaintain the deflection or oscillation at a constant pre-set value. Itis this feedback that is typically used to generate an AFM image.

AFMs can be operated in a number of different imaging modes, includingcontact mode where the tip of the cantilever is in constant contact withthe sample surface, and oscillatory modes where the tip makes no contactor only intermittent contact with the surface.

Actuators are commonly used in AFMs, for example to raster the probe orto change the position of the cantilever base relative to the samplesurface. The purpose of actuators is to provide relative movementbetween different parts of the AFM; for example, between the probe andthe sample. For different purposes and different results, it may beuseful to actuate the sample, the tip, or some combination of both.Sensors are also commonly used in AFMs. They are used to detectmovement, position, or other attributes of various components of theAFM, including movement created by actuators.

For the purposes of the specification, unless otherwise specified, theterm “actuator” refers to a broad array of devices that convert inputsignals into physical motion, including piezo activated flexures, piezotubes, piezo stacks, blocks, bimorphs, unimorphs, linear motors,electrostrictive actuators, electrostatic motors, capacitive motors,voice coil actuators and magnetostrictive actuators. The term “positionsensor” or “sensor” refers to a device that converts a physicalparameter such as displacement, velocity or acceleration into one ormore signals such as an electrical signal, including capacitive sensors,inductive sensors (including eddy current sensors), differentialtransformers (such as described in co-pending applicationsUS20020175677A1 and US20040075428A1, Linear Variable DifferentialTransformers for High Precision Position Measurements, andUS20040056653A1, Linear Variable Differential Transformer with DigitalElectronics, which are hereby incorporated by reference in theirentirety), variable reluctance, optical interferometry, opticaldeflection detectors (including those referred to above as a PSD andthose described in co-pending applications US20030209060A1 andUS20040079142A1, Apparatus and Method for Isolating and MeasuringMovement in Metrology Apparatus, which are hereby incorporated byreference in their entirety), strain gages, piezo sensors,magnetostrictive and electrostrictive sensors.

SUMMARY

Systems and techniques provided herein allow for much more effectivemeasurement of the topography of small surface features than is possiblewith currently available commercial tools. The techniques make judicioususe of inspection time, where more time is devoted to regions of thesample where the highest spatial resolution is desired and less time inother regions where some information may be required, but with lessprecision or spatial resolution.

In one aspect, the current disclosure provides a novel cantilever-basedinstrument that permits more accurate imaging of sample features in ashorter period of time, in which the scan rate is variable over thefield of a single acquired image.

In another aspect, the current disclosure provides a novelcantilever-based instrument that can acquire a single image whichmeasures features with different sizes with a variable pixel densitychosen to balance the competing requirements of high data density andshort measurement time.

In another aspect, the current disclosure provides systems andtechniques to reduce the amount of data acquired and saved bycantilever-based instruments performing metrology operations.

In general, in another aspect, the current disclosure provides a methodcomprising receiving information indicative of a position of a region ofinterest of a sample and generating a scan waveform including a firstwaveform segment configured to obtain a first data density in the regionof interest of the sample and a second waveform segment configured toobtain a second data density less than the first data density outsidethe region of interest of the sample. The scan waveform may furthercomprise a third waveform segment configured to obtain a third differentdata density.

The method may further include scanning a measurement instrumentrelative to the sample using the scan waveform. Scanning the measurementinstrument relative to the sample using the scan waveform may comprisescanning the measurement instrument along a fast scan axis. Scanning themeasurement instrument along the fast scan axis may comprise using thefirst waveform segment to scan the measurement instrument along a firstscan segment and using the second waveform segment to scan themeasurement instrument along a second scan segment. The first scansegment and the second scan segment may be substantially linear.

The scanning waveform may further comprise a third waveform segmentconfigured to obtain a third data density in the region of interest ofthe sample and a fourth waveform segment configured to obtain a fourthdata density less than the third data density outside the region ofinterest of the sample. Scanning the measurement instrument relative tothe sample using the scan waveform may further comprise scanning themeasurement instrument along a slow scan axis, and scanning themeasurement instrument along the slow scan axis may comprise using thethird waveform segment to scan the measurement instrument along a thirdscan segment and using the fourth waveform segment to scan themeasurement instrument along a fourth scan segment.

Scanning the measurement instrument relative to the sample using thescan waveform may comprise scanning the measurement instrument along aslow scan axis, and scanning the measurement instrument along the slowscan axis may comprise using the first waveform segment to scan themeasurement instrument along a first scan segment and using the secondwaveform segment to scan the measurement instrument along a second scansegment. The measurement instrument may be an atomic force microscope.

In general, in another aspect, an apparatus comprises a measurementinstrument including a portion configured to interact with a sample inoperation, a sample holder configured to position the sample relative tothe portion of the measurement instrument, and a controller configuredto provide relative scanning between the measurement instrument and thesample holder. The controller may be configured to provide relativescanning in a first direction, and the relative scanning may include afirst scan segment to obtain a first data density in a pre-determinedsample region and a second scan segment to obtain a second differentdata density outside of the pre-determined sample region.

The controller may be configured to control the sample holder and/or tocontrol the measurement instrument. The apparatus may further comprise adata element in communication with the controller, the data elementincluding at least one of data and instruments to determine a scanwaveform including the first scan segment and the second scan segment.

In general, in another aspect, the current disclosure provides anarticle comprising a machine-readable medium embodying informationindicative of instructions that when performed by one or more machinesresult in operations comprising receiving information indicative of aregion of interest of a sample, and determining a scan rate profile forrelative scanning of a measurement instrument across the sample. Thescan rate profile may include a first scan rate segment associated withthe region of interest and a second scan rate segment associated with aregion of the sample not included in the region of interest, wherein thefirst scan rate segment is configured to implement relative scanning ata denser rate than the second scan rate segment. The first scan ratesegment may be configured to implement linear scanning. The operationsmay further comprise receiving measurement data indicative of one ormore sample parameters for a scan using the scan rate profile. Theoperations may further comprise determining the one or more sampleparameters using the measurement data and the scan rate profile.

In general, in another aspect, the current disclosure provides a methodcomprising implementing relative scanning of a portion of a measurementinstrument with respect to a sample surface, wherein the sample surfaceincludes a first region and a second region. Implementing relativescanning of the portion of the measurement instrument relative to thesample surface may include implementing relative scanning according to awaveform having a first higher data density segment associated withrelative scanning of the first region and a second lower data densitysegment associated with relative scanning of the second region. Themethod may further comprise receiving information indicative of one ormore sample characteristics for the first region and the second regionbased on the relative scanning of the portion of the measurementinstrument with respect to the sample surface.

The sample surface may comprise a sample surface of a sample of a firstsample type, and the first region may be a region of interest for thefirst sample type. The measurement instrument may comprise an atomicforce microscope.

In general, in another aspect, the current disclosure provides a methodcomprising the receipt of information indicative of a relative positionof a first region and a second different region for a particular sampletype, and generating information indicative of a scan waveform includinga first data density waveform portion and a second data density waveformportion. The scan waveform may be configured to obtain a first higherdata density in the first region using the first data density waveformportion and to obtain a higher different data density in the secondregion using the second data density waveform portion.

The particular sample type may be a semiconductor device sample type,and the first region may be a particular region of a circuit included ina semiconductor device formed on a semiconductor substrate. The secondregion may be a reference region of the semiconductor substrate includedin or separate from the circuit. The method may further comprise usingthe information indicative of the scan waveform in a scan of a samplehaving the sample type.

These and other features and advantages of the present invention will bemore readily apparent from the detailed description of the exemplaryimplementations set forth below taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a normal scan waveform for the fast axis of an AFM.

FIG. 2 is an image and software zoom of a two dimensional diffractiongrating acquired with the normal fast-axis scan waveform shown in FIG.1.

FIG. 3 is a dual density scan waveform for the fast axis of an AFM.

FIG. 4 is an image and software zoom of a two dimensional diffractiongrating acquired using the dual density fast-axis scan waveform shown inFIG. 3.

FIG. 5 is a side by side comparison of the software zooms using thenormal and dual density scanning methods.

FIG. 6 shows an implementation of a system that may be used to implementvariable density scanning, according to some embodiments.

FIG. 7 shows an implementation of a system that may be used to implementvariable density scanning, according to some embodiments.

FIGS. 8A and 8B are schematic diagrams of a system that may be used forvariable density scanning, according to some embodiments.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Accurate characterization of a sample by a scanning probe instrumentsuch as an AFM is often limited by the ability of the AFM to move thebase of the cantilever vertically in the Z direction relative to thesample surface at a rate sufficient to characterize the sampleaccurately while scanning horizontally (e.g., in either the X or Ydirection). This movement rate is often expressed in terms of bandwidth.Typical commercial AFM bandwidths at present are on the order of a fewkHz. This implies that, for example, completing a 256.times.256 pixelimage requires a few minutes. This amount of time has typicallyprecluded AFMs from becoming routine in-line inspection systems forindustrial processes. This is especially true when they are competingwith optical inspection tools that may be able to make a similarmeasurement in a fraction of a second.

However, as dimensions of components continue to shrink, criticaldimension (CD) measurements in industrial process and other applicationsthat were formerly accomplished with optical inspection systems are moredifficult and, in some cases, no longer possible.

The dynamic range of CD measurements required is also increasing. Forexample, while the size of devices such as computer chips or magneticrecording heads ranges from .about.100 microns up to about a centimeter,the dimensions of the features of these devices need to be controlled onthe order of a few atomic layers. This can require sub-angstrom standarddeviations in CD measurements. Moving from 100 microns to 1 angstrom isa six order of magnitude range in measurement scales. This range putsstrict performance criteria on the measurement apparatus. The actuatorthat is used to scan the cantilever relative to the sample over a 100micron range is also required to position the probe with sub-nanometeraccuracy and precision.

Some cantilever-based instruments that have been used for CDmeasurements of these sorts of features make use of open-loop piezoscanners. These scanners are subject to numerous limitations. Two of themost problematic are creep and hysteresis. Creep is the uncontrolledmotion of the piezo actuator when the control signal is held stationary.Hysteresis is the label used to describe the unpredictable response ofthe piezo actuator that depends on both the control signal and where theactuator was originally positioned. Overcoming the creep and hysteresisthat are intrinsic to piezo scanners has been the subject of an enormousbody of research and development, principally centered on predictivemodeling of piezo behavior and then linearizing the motion andcorrecting for creep with nonlinear and time dependent command voltages.Unfortunately, understanding the behavior of piezo materials has provendifficult. Worse yet, the behavior can change over time, necessitatingthat this change in behavior be predicted or, more likely, that thepredictions themselves be changed from time-to-time when it is evidentthat the change in behavior has occurred.

Another method of overcoming creep and hysteresis is to provide sensorsthat directly measure the piezo position and then, through the use of afeedback loop, actively correct for any errors in the position. Thisgeneral methodology is referred to as “closed loop” piezo control. Thismethod puts much of the performance demand on the sensors. It isgenerally advantageous if the sensors are linear, operate over anextended dynamic range (.about.100 microns down to less than anangstrom) and be stable over time. Co-pending applicationsUS20020175677A1, US20040075428A1 and US20040056653A1, which have beenincorporated herein by reference, describe a low noise, lineardifferential transformer and signal conditioning that provides theperformance necessary for these sorts of positioning requirements.

As mentioned above, another requirement for CD measurements is that themeasurements be made rapidly. Older, high speed techniques based onoptics are less and less suitable as the length scale of features dropsbelow a few hundred nanometers. This presents manufacturers with aserious throughput problem. Unless new techniques can be made tofunction at speeds approaching those of optical techniques, use of thesetechniques may require testing at less frequent intervals in themanufacturing process.

FIG. 1 is a typical scan waveform for an atomic force microscope. Inthis plot, the position of the scanner for the fast scan axis (theX-axis in this case) is shown. This waveform could result fromnonlinear, open loop voltages being applied to the scanner, orpreferably, from a closed loop methodology. As the scanner rasters backand forth, there are linear regions 1 in the trace and 2 in the retracedirections. These linear regions are separated by non-linear turn aroundregions 3 where the scanner changes direction. It is convenient for dataprocessing to use data only from the linear regions in constructing animage.

FIG. 2 shows an image 4 of a two dimensional diffraction grating whichwas acquired using the fast scan axis waveform of FIG. 1, as well as asoftware zoom 5 into a region of interest of the image. The image 4measures 512 times 4096 pixels. The long axis was made at a scan rangeof 50 μm and the short at 12.5 μm. This yielded square pixels roughly 10nm wide. At a scan rate of 2.5 Hz, it took roughly 3.5 minutes toacquire the image. The 10 nm resolution is apparent in the software zoom5. This zoom is roughly 2 μm square and thus made up of 200 times 200pixels.

It should be noted that the rectangular aspect ratio of image 4 in FIG.2 represents one common way AFMs have reduced image acquisition time. Byusing non-square scanning, the acquired data more closely matches thearea of interest on the device. Although this may provide some benefits,it may not be sufficient for some applications.

Systems and techniques provided herein allow for tuning the dataacquisition density to the particular requirements of differentmeasurements in the operation of measurement instruments (such ascantilever-based instruments), thereby improving the acquisition time,accuracy and precision of the measurement. Herein, “data density” refersto the amount of data acquired per sample surface unit (per relativeprobe-sample distance traversed, sampled surface area, or otherappropriate sample surface measurement.)

Much current AFM research and development involves speeding up themeasurement bandwidth of these cantilever-based instruments. The presentdisclosure, however, concerns using an AFM in a “smarter” manner. Inaccordance with embodiments of the invention, by tuning the data densityto the particular measurement requirements, the acquisition time and, asit turns out, the accuracy and precision of the measurement can begreatly improved.

Moreover, the current systems and techniques provide for increased datadensity without increasing the data acquisition time, by using one ormore scan waveforms with at least one high density waveform segment andat least one lower density waveform segment. Therefore, the currenttechniques may be used in environments in which existing techniques arenot practical.

Referring again to the example of FIG. 2, the region depicted in thesoftware zoom 5 might, for example, be particularly important forproduction tolerances. Higher data density for this region would bedesirable. Rather than assessing each sample individually anddesignating particular regions as interesting, this region may bedesignated ahead of time as a region of interest for each sample of thesample type represented by FIG. 2.

Furthermore, the features in the other regions of the sample are not ascritical. Though it is important to have some information about thoseregions, the point density can be much lower. In fact, in some existingsystems, data from less interesting regions is obtained and thenlow-pass filtered, effectively throwing away information after it wasacquired. This is a consequence of conventional scanning methods. For agiven AFM mechanical bandwidth, the only way to get better data densityin the region of interest using a conventional raster scan waveform isto slow the scan rate down and acquire more points over the entireimage. This results in an undesirably long acquisition time and datafiles that are much larger than they need to be.

FIG. 3 shows a waveform according to one of the embodiments of thepresent invention. In this embodiment, there are two types ofacquisition regions, low density trace 6 and retrace 7 regions and highdensity trace 8 and retrace 9 regions. These regions are separated bytransition regions 10, 11 and 12. For ease of comparison, the total scanrange of the curve shown in FIG. 3 is the same as that shown in FIG. 1.The illustrated scans, in fact, take the same amount of time (roughly 1second). However, the probe now spends less time in the low densityregions 6 and 7, and much more time in the high density regions 8 and 9.

FIG. 4 shows the results of this scan on the same diffraction gratingpictured in FIG. 2. The 12.5.mu.m.times.50.mu.m image 14 of the gratinglooks quite similar to the image 4 of the same grating in FIG. 2.However, the pixels in 14 and the software zoom 15 are now no longersquare, nor are they uniformly sized over the image. The software zoom15 of FIG. 4 shows the resulting enhanced resolution over the region ofinterest, the same region shown in the software zoom 5 of FIG. 2.

FIG. 5 shows a side by side comparison of the two software zoomedregions 5 and 15. The dual density scan 15 clearly shows more detailthan the conventionally acquired image 5, even though the imageacquisition times and file sizes for the two images are identical.

The embodiment of the present invention depicted in FIG. 3 and FIG. 4shows a case where only the scan rate of the fast axis (in this case,the x-axis) was varied. In another embodiment, the slow scan rate (they-axis, when the x-axis is the fast axis) can also be varied as well,either separately or in combination with the fast scan axis.

The display of the image data can be accomplished in a number of ways.For example, in FIG. 4, the pixels were plotted versus spatial position.The data could also be plotted versus time, in which case the slow scanregions would be displayed as spatially zoomed.

FIG. 6 shows an embodiment of a measurement system incorporating thetechniques described above. A sample 610 is attached to a z-actuator 620(“z” here represents that the actuator moves in the vertical direction)and the base 670 of a flexible cantilever 660 is attached to xy-actuator680 (“xy” here represents that the actuator moves in the horizontal xyplane) which is attached to a head frame 690 or to the z-actuator 620,such alternative being indicated by lines from the xy-actuator 680 tothe head frame 690 and the z-actuator 620 (it being understood that thexy-actuator 680 is attached either at one of these places or the other,but not both). Here, x and y are two non-parallel directions in thehorizontal plane (e.g., orthogonal directions in the horizontal plane),while z is a direction not in the xy plane (e.g., the vertical directionorthogonal to the xy plane). The xy-actuator 680, combined with thez-actuator 620, provides relative motion between a probe 650 and thesample 610 in all three dimensions. The cantilever 660 deflects inresponse to interactions between the probe 650 of the cantilever 660 andthe sample 610. This deflection is measured by a PSD 700. The output ofthe PSD 700 is collected by the controller 710. Typically, thecontroller 710 performs some processing of the signal, extractingquantities such as the cantilever deflection, amplitude, phase or otherparameters. These values are often displayed on a display device 720.Furthermore, the controller 710 can operate a feedback loop that in turnvaries the relative position of the base 670 of the cantilever 660 andthe sample 610 in response to sample characteristics. For this purpose,the controller 710 sends control signals to the xy-actuator 680 and thez-actuator 620. In one embodiment, the xy-actuator 680 includes aposition sensor that allows closed loop feedback positioning control.

An example where the x-axis is the fast scan axis and xy-actuator 680may implement a scanning waveform having a first substantially linearregion with a first slope, and a second substantially linear region witha second different slope, is illustrated in the embodiment depicted inFIG. 3.

In other embodiments, the scan may be performed using a waveform thatdoes not have linear regions. However, it is often useful to have linearregions with different scan rates separated by non-linear transitionregions. Transition regions such as these allow the behavior of thescanner to be improved, to reduce ringing and allow closed loop feedbackcontrol, the preferable feedback methodology, to work efficiently.

FIG. 7 shows another embodiment of a system that may be used toimplement the techniques described above. In FIG. 7, controller 710 isin communication with an xy-actuator 680 to which a sample 610 isattached so that the probe 650 of cantilever 660 is scanned relative tothe surface of sample 610 using waveforms such as those described above.The frame of the microscope base 685 could contain other coarsepositioning elements such as manual or motorized mechanical translationstages. In this embodiment, the cantilever 660 and its base 670 areactuated in the z-direction by actuator 620 which is in communicationwith the controller 710. Motion of the cantilever 660 is detected by adetector 750 that can either be fixed relative to the head frame 690 orrelative to the cantilever base 670.

In addition to the embodiments described here, there are numerous otherinstruments that could benefit from the systems and techniques describedhere. In particular, this includes AFMs configured for larger samples orfor industrial measurements such as those described in U.S. Pat. Nos.6,945,100, 6,677,567, 6,612,160, 6,530,268, 6,032,518, 5,714,682,5,560,244 and 5,463,897, and in US patent applications 20040079142A1 and20030209060A1 (which have been incorporated herein by reference).

Although it is advantageous to use closed loop scanners for thesemetrology measurements, it is not required. In some cases, it may besufficient and even advantageous to use an arrangement where theperformance of an open loop scanner is augmented by the addition of aclosed loop scanner capable of performing the scanning waveformsdescribed here. Scanners such as these are currently commerciallyavailable under the trade name “npoint” and include the XY scanner withtrade name NPXY100A and similar systems.

FIG. 8A shows an embodiment of a measurement system 800 incorporatingthe techniques described above. System 800 includes a sample 810positioned on a sample holder 820. A measurement instrument 830 isconfigured to obtain information across sample 810. Instrument 830 isscanned across the surface of sample 810 using a controller 840.

Sample data is obtained using a detector 850, which may be a PSD orother detector. Information indicative of one or more samplecharacteristics (such as topographical characteristics, magneticcharacteristics, electrical characteristics, etc.) may be provided to adata storage and/or processing unit 860 (which may comprise a singleunit or multiple units, and may be at least partially integrated withother elements of system 800). Processing unit 860 may also includesoftware and/or hardware (as well as other means known to those versedin the art) to make use of data to control scanning of instrument 830,according to the embodiments of the invention provided herein.

For an example where the x-axis is the fast scan axis, processing unit860 may include data causing controller 840 to implement a waveformhaving a first substantially linear region with a first slope, and asecond substantially linear region with a second different slope, asillustrated in the embodiment illustrated in FIG. 3.

In other embodiments, the scan may be performed using a waveform thatdoes not have linear regions as has been discussed above in connectionwith the description of the embodiment depicted in FIG. 6.

FIG. 8B shows another embodiment of a system 801 that may be used toimplement the techniques described above. In FIG. 8B, controller 840 isin communication with sample holder 820, and may control holder 820 sothat instrument 830 is scanned across the surface of sample 810 usingwaveforms such as those described above. Controller 840 (which may be asingle unit, may be multiple units, and/or may be at least partiallyintegrated with another part of system 801) may also control instrument830, if desired. However, control of either instrument 830 or sampleholder 820 in the scanning plane may simplify operation of system 801.

The measurements for which the systems and techniques provided hereinare potentially useful include a wide variety of metrology applicationswhere precise measurements of small features referenced specifically tonearby larger features are desirable or where, in an automatedproduction process, a particular step is continued until the componenttolerances, as measured by the above systems or techniques are deemed tobe within specification. Examples include semiconductor and electronicdevice process controls such as chemo-mechanical polishing (CMP),surface flatness, surface waviness, surface finish quality, planarity,step and feature heights, and height differences (to name a few). Inaddition to semiconductor manufacturing, there are numerous other fieldswhere this technique could be used including optics,micro-electromechanical (MEMS) devices and data storage devices.

The systems and techniques provided herein can be combined with manyother surface measurement and observation instruments. For example,features could be identified with an optical microscope, interferometer,scatterometer, ellipsometer, bright or dark field microscope, Ramanmicroscope or optical profiler. These features could then be registeredas regions of interest for inspection with a cantilever-basedinstrument. The regions of interest could then be linked to high datadensity image regions in the cantilever-based instrument. Thiscombination could, for example, be used for defect detection or defectreview of a semiconductor or other type of wafer where opticaltechniques are used to identify defects. The systems and techniquesprovided herein can then be used in conjunction with the opticalinformation to describe a region of interest where high resolution datais useful and where lower resolution data in the neighborhood of theregion of interest is also of use. More detailed information on thedefect or other feature can then be acquired and displayed according tothe above discussion.

This selective region of interest examination technique has obviousapplications in the conventional semiconductor industry but also inother manufacturing industries. The dimensions of high brightness LEDs,CMOS and other imaging sensors (cameras), special coatings on glass orother substrates (indium-tin oxide), liquid crystal or other displaytechnologies, SiC and GaN based Shottky diodes and field effecttransistors (FETs) are all shrinking, leading to more stringentmetrology requirements.

The discussion of systems and techniques herein has focused mainly onthe application of these systems and techniques to topographymeasurements. Cantilever-based instruments are capable of many othertypes of measurements as well, either independent of or associated withtopography measurements. These include DC contact mode imaging and ACmodes including phase imaging, force modulation, sample stiffness,magnetic forces and interactions and dissipation, electricalcharacterization such as tunneling current, conductivity, capacitance,spreading resistance, electric force, Kelvin force, potential,dissipation, and numerous other modes described in the AFM literature.

Extending the systems and techniques provided herein and illustratedwith topography examples to these and other additional measurements nowconventional with cantilever-based instruments is straightforward.Examples include magnetic force microscopy, dissipation, phase imaging,thermal scanning, magnetic sensitivity mapping, tunneling microscopy,conductive AFM, scanning capacitance, Kelvin force, scanning potentialmicroscopy, scanning electrochemical or ion conductance microscopy andscanning near field optical microscopy. This list is only a partial listof available other modes, any of which could benefit from the systemsand techniques described here. A region of interest in one or more ofthese information channels is very similar to the idea of a region ofinterest in topography. In some cases, the region of interest might bespatially located at the same physical location, in others it could beoffset by some prescribed distance.

The above described techniques and their variations may be implementedat least partially as computer software instructions. Such instructionsmay be stored on one or more machine-readable storage media or devicesand are executed by, e.g., one or more computer processors that causethe measurement instrument to perform the described functions andoperations.

A number of implementations have been described. Although only a fewimplementations have been disclosed in detail above, other modificationsare possible, and this disclosure is intended to cover all suchmodifications, and most particularly, any modification which might bepredictable to a person having ordinary skill in the art.

Also, only those claims which use the word “means” are intended to beinterpreted under 35 USC 112, sixth paragraph. In the claims, the word“a” or “an” embraces configurations with one or more elements, while thephrase “a single” embraces configurations with only one element,notwithstanding the use of phrases such as “at least one of” elsewherein the claims. Moreover, no limitations from the specification areintended to be read into any claims, unless those limitations areexpressly included in the claims. Accordingly, other embodiments arewithin the scope of the following claims.

1. A method of controlling a cantilever based scanning instrument thatdetermines information about a measured surface, comprising: scanningthe cantilever across the measured surface in first and secondorthogonal directions across the surface, while obtaining scaninformation from said first orthogonal direction, and where saidscanning in said first direction uses at least a first scanning speedconfigured to obtain first data at a first data density in a firstregion of the sample and a second scanning speed configured to obtainsecond data at a second data density less than the first data density ina second region of the sample, and using said first data and said seconddata in a measurement device to obtain sampled information about saidsurface.
 2. The method as in claim 1, wherein said scanning comprisesscanning in a raster fashion back and forth across said surface, toprovide a plurality of raster scans in a first coordinate directionacross said surface.
 3. The method as in claim 2, wherein each of aplurality of said raster scans in said first coordinate direction haveboth said first scanning speed and said second scanning speed.
 4. Themethod as in claim 3, wherein said first scanning speed is in the samefirst area in each of said plurality of raster scans.
 5. The method asin claim 2, wherein said first coordinate direction is the direction ofa fast scan axis.
 6. The method as in claim 1, further comprisingobtaining, in a scan controller, information indicative of a position ofa region of interest of a sample; and wherein said first region is saidregion of interest.
 7. The method as in claim 3, further comprisingcreating a scan waveform by said scan controller and said scan waveformbeing used for each of said plurality of raster scans, and said scanwaveform being configured to obtain higher density in said first regionby scanning slower in said first region along each of said plurality ofraster scans.
 8. The method as in claim 7, wherein said scan waveformincludes first and second linear scan segments.
 9. The method as inclaim 1, wherein the scanning waveform further comprises a thirdwaveform segment configured to obtain a third data density in the regionof interest of the sample and a fourth waveform segment configured toobtain a fourth data density less than the third data density outsidethe region of interest of the sample, and wherein the scanning themeasurement instrument relative to the sample using the scanningwaveform further comprises scanning the measurement instrument along aslow scan axis, and wherein scanning the measurement instrument alongthe slow scan axis comprises using the third waveform segment to scanthe measurement instrument along a third scan segment and using thefourth waveform segment to scan the measurement instrument along afourth scan segment.
 10. The method of claim 1, wherein the measurementinstrument is an atomic force microscope.
 11. A cantilever basedscanning instrument that determines information about a measuredsurface, comprising: a cantilever; a cantilever scanning device scanningthe cantilever relative to the measured surface according to a scanningcontrol signal; a controller, creating said scanning control signal toscan the cantilever in first and second orthogonal directions across thesurface, while obtaining scan information from said first orthogonaldirection, and where said scanning in said first direction uses at leasta first scanning speed configured to obtain first data at a first datadensity in a first region of the sample and a second scanning speedconfigured to obtain second data at a second data density less than thefirst data density in a second region of the sample; and a measurementdevice to obtain sampled information about said surface based on saidfirst data and said second data.
 12. The instrument as in claim 11,wherein said scanning control signal controls scanning in a rasterfashion back and forth across said surface, to provide a plurality ofraster scans in a first coordinate direction across said surface. 13.The instrument as in claim 12, wherein each of a plurality of saidraster scans in said first coordinate direction have both said firstscanning speed and said second scanning speed.
 14. The instrument as inclaim 13, wherein said first scanning speed is in the same first area ineach of said plurality of raster scans.
 15. The instrument as in claim12, wherein said first coordinate direction is the direction of a fastscan axis.
 16. The instrument as in claim 11, further comprisingobtaining, in a scan controller, information indicative of a position ofa region of interest of a sample; and wherein said first region is saidregion of interest.
 17. The instrument as in claim 14, wherein saidscanning control signal is used for each of said plurality of rasterscans, and said scanning control signal m being configured to obtainhigher density in said first region by scanning slower in said firstregion along each of said plurality of raster scans.
 18. The instrumentas in claim 17, wherein said scanning control signal includes first andsecond linear scan segments.
 19. The instrument as in claim 15, whereinsaid first coordinate direction is the “x” direction.
 20. The instrumentof claim 11, wherein the measurement instrument is an atomic forcemicroscope.
 21. The instrument of claim 11, wherein the scan waveformfurther comprises a third waveform segment configured to obtain a thirddata density in the same scanning waveform that obtains said first andsecond data densities.
 22. The instrument of claim 11, whereincantilever scanning device is configured to control a sample holder. 23.The instrument of claim 11, wherein cantilever scanning device isconfigured to control the measurement instrument.
 24. An articlecomprising a non-transitory machine-readable medium embodyinginformation indicative of instructions that when performed by one ormore machines result in computer implemented operations comprising:scanning the cantilever across a surface in first and second orthogonaldirections across the surface, while obtaining scan information fromsaid first orthogonal direction, and where said scanning in said firstdirection uses at least a first scanning speed configured to obtainfirst data at a first data density in a first region of the sample and asecond scanning speed configured to obtain second data at a second datadensity less than the first data density in a second region of thesample, and using said first data and said second data in a measurementdevice to obtain sampled information about said surface.
 25. The articleas in claim 24, wherein said scanning comprises scanning in a rasterfashion back and forth across said surface, to provide a plurality ofraster scans in a first coordinate direction across said surface. 26.The article as in claim 25, wherein each of a plurality of said rasterscans in said first coordinate direction have both said first scanningspeed and said second scanning speed.
 27. The article as in claim 26,wherein said first scanning speed is in the same first area in each ofsaid plurality of raster scans.
 28. The article as in claim 25, whereinsaid first coordinate direction is the direction of a fast scan axis.29. The article as in claim 24, further comprising obtaining, in a scancontroller, information indicative of a position of a region of interestof a sample; and wherein said first region is said region of interest.30. The article as in claim 27, further comprising creating a scanwaveform by said scan controller and said scan waveform being used foreach of said plurality of raster scans, and said scan waveform beingconfigured to obtain higher density in said first region by scanningslower in said first region along each of said plurality of rasterscans.
 31. The article as in claim 30, wherein said scan waveformincludes first and second linear scan segments.
 32. The article as inclaim 31, wherein the scanning waveform further comprises a thirdwaveform segment configured to obtain a third data density in the regionof interest of the sample and a fourth waveform segment configured toobtain a fourth data density less than the third data density outsidethe region of interest of the sample, and wherein the scanning themeasurement instrument relative to the sample using the scan waveformfurther comprises scanning the measurement instrument along a slow scanaxis, and wherein scanning the measurement instrument along the slowscan axis comprises using the third waveform segment to scan themeasurement instrument along a third scan segment and using the fourthwaveform segment to scan the measurement instrument along a fourth scansegment.
 33. The article of claim 24, wherein the measurement instrumentis an atomic force microscope.